Preheat oven to 350° F. Spray a 9×9-inch baking dish with nonstick cooking spray.
In a medium skillet over medium heat, add the olive oil. Add bell pepper, onion and zucchini. Sauté until tender, then add garlic and spinach. Cook until wilted.
Beat the eggs in a bowl and add the vegetables, cheese, salt and pepper. Pour mixture into prepared baking dish.
Bake 25 to 30 minutes, until fully set. Allow to cool.
Cut into 6 strips crosswise, then once down the middle lengthwise to create 12 pieces. Serve.
Refrigerate leftovers in an airtight container up to 4 days.
Make ahead of time and freeze. Place cooled frittata fingers in a freezer bag and lay flat until frozen. When ready to eat, microwave 60 to 90 seconds, or until warmed.